It is proved that SRGM based on NHPP type of G-O model doesn't need to consider imperfect debugging and new mistakes during the debugging process. A new type of SRGM comes out which does not only consider the software developer's familiarity with software system, but also consider the diminishing mistakes developing system. This SRGM has considered the fault detection rate changing with the time changing. Moreover, the test result by using the public reported data shows that the goodness of fit is better than that of other models of G-O model.